[SCIP] Could you please tell me what is a pesudo solution (non-fixed integer solution) ?

[朱外明]

Dear Ambros,


    Thanks very much for your kind answering me on foregoing questions. Now my program is OK on running but abnormal on solving the problem. At the begining of branch and price, SCIP would produce pesudo solutions (non-fixed integer solutions). As a result, I must realize a BRANCHEXECPS branching method (I used the SCIPbranchVar method inside this branching). Then the searching steps into BRANCHEXECLP branching in which fractional variable values are available. 


    Here is something difficult to be understood. What is a pesudo solution? Does not SCIP solve the linear relaxation of master problem directly? If yes, fractional variable values should be avalaible at the root node. Why it is not the truth from my experience? Dear Ambros, could you please tell me something about this ?


    Some displaying information are listed:


--------------------------------------------------------------------------------------------------------------------------
SCIP> read data/data.scp
read problem <data/data.scp>
============
original problem has 5 variables (5 bin, 0 int, 0 impl, 0 cont) and 15 constraints
SCIP> optimize
feasible solution found by trivial heuristic after 0.0 seconds, objective value 5.000000e+04
presolving:
   (0.0s) probing cycle finished: starting next cycle
presolving (1 rounds: 1 fast, 1 medium, 1 exhaustive):
 0 deleted vars, 0 deleted constraints, 0 added constraints, 0 tightened bounds, 0 added holes, 0 changed sides, 0 changed coefficients
 0 implications, 0 cliques
presolved problem has 5 variables (5 bin, 0 int, 0 impl, 0 cont) and 15 constraints
     15 constraints of type <setppc>
transformed objective value is always integral (scale: 1)
Presolving Time: 0.01
transformed 1/1 original solutions to the transformed problem space
 time | node  | left  |LP iter|LP it/n| mem |mdpt |frac |vars |cons |cols |rows |cuts |confs|strbr|  dualbound   | primalbound  |  gap  
  0.0s|     1 |     0 |    12 |     - | 918k|   0 |   0 | 110 |  15 | 110 |  15 |   0 |   0 |   0 |      --      | 5.000000e+04 |    Inf
r 0.0s|     1 |     0 |    12 |     - | 921k|   0 |   0 | 110 |  15 | 110 |  15 |   0 |   0 |   0 |      --      | 5.000000e+00 |    Inf
  0.0s|     1 |     0 |    12 |     - | 921k|   0 |   0 | 110 |  15 | 110 |  15 |   0 |   0 |   0 |      --      | 5.000000e+00 |    Inf
[src/branch_scp.c:219] debug: start BRANCHEXECPS branching !
[src/branch_scp.c:356] debug:  -> 110 candidates, selected candidate 109: variable <>
  0.0s|     1 |     2 |    12 |     - | 922k|   0 |   0 | 110 |  15 | 110 |  15 |   0 |   0 |   0 |      --      | 5.000000e+00 |    Inf
[src/branch_scp.c:219] debug: start BRANCHEXECPS branching !
[src/branch_scp.c:356] debug:  -> 109 candidates, selected candidate 108: variable <>
[src/branch_scp.c:219] debug: start BRANCHEXECPS branching !
......
[src/branch_scp.c:356] debug:  -> 62 candidates, selected candidate 61: variable <>
[src/branch_scp.c:219] debug: start BRANCHEXECPS branching !
[src/branch_scp.c:356] debug:  -> 61 candidates, selected candidate 60: variable <>

[src/branch_scp.c:77] debug:  start BRANCHEXECLP branching ![src/branch_scp.c:85] debug: start branching at node 96, depth 50
.............

--------------------------------------------------------------------------------------------------------------------------


    Thank you.


    With best regards!




-----------------------------------------------
Your sincerely follower, Zhu Waiming
zhuwaiming at mail.hfut.edu.cn
Hefei University of technology, China
orcid.org/0000-0001-7134-6584
https://www.researchgate.net/profile/Zhu_Waiming
2017-12-04



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